DE-FC26-06NT42962

Project Goal

The goal of this project is to characterize and quantify the postulated gas hydrate resource associated with the Barrow Gas Fields – three producing fields located in a permafrost region near Barrow, the North Slope's biggest population center and economic hub.

Map of the North Slope Borough showing the location of its eight major communities,
including Barrow, the site of this research project.

Background

The North Slope Borough (NSB) of Alaska comprises an area of 89,000 square miles. Eight communities are located in the NSB including Barrow, Point Lay, Point Hope, Wainwright, Atqasuk, Nuiqsut, Kaktovik, and Anaktuvuk Pass. Barrow is the largest city and serves as the economic, transportation and administrative center for the Borough.

The NSB contains significant known and potential energy resources, including the National Petroleum Reserve-Alaska (NPR-A) and the Prudhoe Bay, Kuparuk, Endicott, Alpine and Milne Point oil fields. The NSB Department of Public Works Energy Management Group oversees production from the Barrow Gas Fields (i.e., East Barrow, South Barrow and Walakpa Fields) which provide heating and electricity for the approximately 4400 residents, businesses and government services in Barrow. Other NSB communities depend on importing fuel at great cost.

Based on recent estimates of remaining reserves and current consumption rates, the Borough’s gas supply should last for over 150 years. However, the demand for energy is expected to grow in Barrow, and the prospect of distributing gas and/or power to outlying villages in the Borough will create increasing pressure on the public utility to increase gas supply to meet demand. Previous research efforts funded by the US Department of Energy (DOE), suggest that accumulations of gas hydrate exist within the Barrow area gas fields. The depletion mechanism of these conventional gas reservoirs is believed to be primarily gas expansion, with potential contributions from edge water drive, and possible recharge from the dissociation of gas hydrate up-dip of the free gas pool. Understanding the drive mechanism is critical to field management, and will impact future development plans, particularly the selection of new development well locations and future compression requirements.

Map of the Barrow Gas Fields operated by the North Slope Borough Department of Public Works Energy Management Group.

There is sufficient data to suggest the presence of gas hydrate in the Barrow Gas Fields. The reservoirs are relatively shallow and in a permafrost region, and reservoir temperatures in places are postulated to be cool enough to support the presence of gas hydrate. Given other favorable conditions (i.e., formation gas composition, formation water chemistry, and reservoir pressure), gas hydrate is likely to exist and is possibly a contributor to the drive mechanism of the reservoirs. However, this has yet to be proven.

The characterization and quantification of methane hydrate resources in the Barrow Gas Fields will be done in two phases. During Phase 1A, the North Slope Borough will build on previous studies to characterize and quantify the methane hydrate resource potential associated with the Barrow Gas Fields. Phase 1A will include information gathering; gas sampling for geochemical analysis; seismic and well log analysis, computer modeling, and documentation and dissemination of information to the DOE and other interested and affected entities. Specifically, Phase 1A will determine if a methane hydrate stability zone exists up-dip of one or more of the Barrow Gas Fields, validating the hypothesis that the gas in question is indeed disassociated methane hydrate rather than free gas.

In Phase 1B, the North Slope Borough will: 1) determine the probability that the reservoir is continuous up-dip into the methane hydrate stability zone and contains sufficient water to combine with available gas to form gas hydrate; 2) determine the optimum well location for a dedicated methane hydrate well; and 3) quantify reserves, expected production rates and depletion mechanisms for methane hydrate production.

If supported by the results of Phase 1, the project may apply for continuation to Phase 2 which will include the design and drilling of a dedicated hydrate well and, possibly, field testing to provide valuable insights into the producibility of hydrate reservoirs. Phase 2 will help to determine the impact of gas hydrate on future free gas production and its viability as an energy source.

Potential Impacts of this research

Findings from this project will contribute significantly to industry’s understanding of the role of gas hydrate in the recharging of a producing gas field and of how free disassociation of hydrates can be utilized as a method for commercial development. This project could also provide substantial economic and social benefits to the North Slope Borough. These benefits include: lower energy costs through an expansion of recoverable gas reserves, the ability to regionalize power generation in the Borough (this will also lower energy costs), and the potential for enhancing the possibility of commercial development of a gas-to-liquids (GTL) facility on the North Slope to provide transportation fuels (diesel) to the area.

Accomplishments
Phase 1A has been completed in which gas hydrate stability modeling was done for the East and South Barrow and Walakpa Gas Fields. Gas analysis data, from recent analyses and from the literature, were utilized to estimate the three phase (water-hydrate-gas) pressure-temperature equilibrium relationship for each field. Other inputs such as pressure and temperature gradient, and water salinity were used to relate hydrate stability zone with reservoir sub-sea depths. For each field the pressure-temperature equilibrium data were estimated considering 0% salt, 2% salt and 4% salt concentrations. The results strongly suggest the existence of a hydrate stable zone within East Barrow Gas reservoir. The results for Walakpa Gas Field are promising as they indicate that the hydrate stable zone exists in up-dip locations within the reservoir. The temperature and pressure conditions of South Barrow are not promising and suggest that that gas hydrates do not occur. Results of the hydrate stability modeling for the South pool indicate that the HSZ is significantly above the known gas sand shallowest penetration, and it is not clear that the reservoir sands extend updip enough to intersect the HSZ.

East Barrow Gas Field Modeled Hydrate Stability Zone

Walakpa Gas Field Modeled Hydrate Stability Zone

Based on the results of Phase 1A, a decision was made by NETL to continue this project into Phase 1B with the goal of fully characterizing the Barrow fields and selecting an optimal site for a potential production test well in the future. Based on geoscience, reservoir and logistical considerations, two locations have been identified for a potential hydrate test well. The wells are situated near the modeled base of hydrate stability zone, ideally intersecting the hydrate/free-gas interface, and they are both located on seismic lines. The primary candidate is in the updip extent of the East Barrow Gas Field, and is favored due to proximity to road access. The second location is updip of the main Walakpa Gas Field, and while more difficult logistically, it benefits from better seismic and well coverage, and therefore more accurate reservoir characterization. The primary location is in East Barrow Gas Field and the secondary site is updip of Walakpa Well #1.

Map of East Barrow Gas Field with Proposed Hydrate Test Well Location

Map of Walakpa Gas Field with Proposed Hydrate Test Well Location

Current Status
1970’s vintage seismic data from the USGS and 1988-89 North Slope Borough Vibroseis data were acquired in order to gain insight into the distribution, thikness and quality of the East Barrow and Walapka gas fields. Available well log and core information were correlated with the seismic to determine reservoir properties. The results of the seismic, well log and core evaluation can be found in the Topical Report, Seismic and Well Log Evaluation of the Barrow High Area, Including the Walapka and Barrow Gas Fields. These data represent a significant improvement in the understanding of the characteristics of the two fields and has been incorporated into an integrated 3-D reservoir model. The model, used for full-field modeling and simulation of the effects of hydrate dissociation, is described fully in the Topical Report, An Integrated Reservoir Model Description for East Barrow and Walapka Gas Fields, Alaska.

In addition to the reservoir simulation, an intermediate modeling step was conducted to determine if the production history performance results for the East Barrow Field could be explained with either volumetric gas expansion, volumetric gas expansion coupled with aquifer support, or hydrate dissociation, gas expansion and aquifer support. The material balance or "tank" modeling results indicated that volumetric expansion could not explain the pressure response of the reservoir, and that pressure support either from an aquifer, methane hydrate dissociation, or a combination of both must be a factor. This was a valuable step that supports the full dynamic reservoir modeling effort. Details of the material balance and ‘tank’ model results can be found in the Topical Report, Material Balance Study to Incestigate Methane Hydrate Resource Potential in the East Pool of the Barrow Gas Field.

Full-scale reservoir simulation was performed for the East Barrow and Walakpa fields to evaluate and quantify methane hydrate resource potential that appears to exist adjacent and up-dip of the free gas producing reservoirs. Geologic models we input into CGM-STARS simulators and history matched. The models were then used to predict future hydrate dissociation to recharge the free gas reservoirs. Model forecasts predict that 100% of the 26 BCF of in-place methane hydrates will be produced from the East Barrow Pool over its production life of 1981-2037 with one additional well and 20% of the 284 BCF of in-place methane hydrates will be produced from the Walakpa Field reservoir over a production life of 1992-2037 using the current production rates from existing wells. Details of the reservoir simulations can be found in the Topical Report, Full Scale Reservoir Simulation Studies for the East Pool of the Barrow Gas Field and the Walapka Gas Field [PDF-11.15MB].

The Phase 1 project is complete and the Final Technical Report is available below under "Additional Information". Phase 2 of the project has been awarded and will commence December 2008. For more information on the Phase 2 project.

Additional Information
In addition to the information provided here, a full listing of project related publications and presentations as well as a listing of funded students can be found in the Methane Hydrate Program Bibliography [PDF].